We've been using SM since January. So what do I think of it now that I have more experience with it?
For #1 (now 9 years old):
I haven't used it with her for a while. I think I had a hard time placing her within the program from the beginning. She got bored with it quickly because it mostly seemed like review. She hates math anyway and I got discouraged. That's when we switched to Time 4 Learning.
A few days ago I looked into the third book (the last of the first set) to see about doing a few pages with her. Again, I just wasn't sure where to place her. So I'll probably just sell the 3rd book to someone who is interested.
We still use the manipulatives.
For #2 (4 years old):
We started Horizons Math for her since I felt she needed something more workbook-y. I was surprised at how well she took to Horizons. I do give the credit to SM for a good beginning foundation. Horizons moves pretty fast and she's not faced any troubles yet.
We're almost to the end of the first book. I plan to continue with it as long as it seems to work. I'll be alternating back and forth between SM and Horizons.
Overall, I think it's great for little ones starting out with Math. It's gentle and fun. I'll use it with #3 when she's ready for Math. I wish #1 had started out with it. That's the only reason I don't think it has worked for her.